The organic light-emitting diode (OLED) elements have the characteristics of having a thin thickness; having a good shock resistance as being solid-state components and easily being adapted to harsh environments; and being mostly self-luminous and without substantial problems of the viewing angle. Therefore, the lighting device applying the OLED element may have advantages. For example, the light source of an OLED device is a diffusion based surface light source, therefore, the light emitted from the OLED device is relatively soft, and has a light and thin appearance. Also, the shape for an OLED device using a flexible substrate may be changed into any of different shapes. Furthermore, for an OLED device using a transparent electrode, the transmittance of the OLED device is like that of a glass when the OLED elements in the OLED device does not emit light. Therefore, the applications of OLED devices may be wider than those of other lighting technologies or devices thereof.
Furthermore, an OLED element is a current-driven element, and a light emitting layer in the OLED element is typically driven by two electrodes as an anode and a cathode, respectively. The anode and the cathode may be, but not limited to two transparent electrodes. Take a transparent electrode as an example, as the area of an OLED device is increased, the impedance of the transparent electrode will also increase with a longer distance. This would cause the emitting light of the OLED device is not uniform, and further produce the heat locally and affect the service life of the OLED device. Accordingly, in order to improve the impedance of the transparent electrode, an auxiliary electrode could be disposed on one of transparent electrodes (for example, the lower one of the transparent electrodes), such that the optical efficiency (for example, light uniformity) of the OLED element could be enhanced.
In general, the auxiliary electrode is formed on a metal wire or a metal mesh on the lower transparent electrode by a printing process, so that the auxiliary electrode could have a rough surface. Once a light emitting layer is formed on the lower transparent electrode and the auxiliary electrode, the light emitted from the light emitting layer disposed on the auxiliary electrode would not be uniformly distributed or it would crack the light emitting layer. So that, the auxiliary electrode would contacts the upper transparent electrode via the crack place of the light emitting layer and a short circuit of the light emitting device would occurs. Nowadays, configuring an insulator layer on the auxiliary electrode is also provided to avoid the aforementioned contact of the auxiliary electrode and the upper transparent electrode.